JP 10-212319A (corresponding to U.S. Pat. No. 6,187,883B) discloses a highly stereoregular olefin polymer produced by polymerizing an olefin in the presence of a polymerization catalyst, the catalyst being formed according to a process comprising the steps of (1) reducing a titanium compound with an organomagnesium compound in the presence of a combination of an organosilicon compound with an ester compound, thereby producing a solid product, (2) contacting the solid product with a halogenation compound, an internal electron donor and an organic acid halide, thereby producing a solid catalyst component containing trivalent titanium atoms, and (3) contacting the solid catalyst component containing trivalent titanium atoms, an organoaluminum compound and an external electron donor.